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[math89]

I read under the Windows Forum that having several (2)i USB DAC playing simultaneously is a problem due to some synchronization problems.
Is that a definitive issue  ? ?

I want to test a multi way system with two iFi IDSD DACS. Electrostatic speakers, down to 50Hz, and then a Muse subwoofer. Let's make a try.

First how can I have them playing music together ?

Regards,
Mathieu

[Arindelle]

I don't think you can. Even if you could, how would the clocks in each DAC pas the information to their analogue sections? I doubt it would be the best sound possible. It hardware related not software related.

On top of that you only have USB as an input choice. You could mess around with bass management and parametric EQ I guess using only 1 of the dacs.

sounds like you should look into a, interface from focusrite, lynx, steinberg -- not sure if they have models that handle DSD though. A tad more money though.

[blgentry]

You can use the Audio MIDI setup tool in OS X to make an "aggregate device" containing both of your DACs.  Then you can use MC to play to the aggregate device and use all of the channels.  It takes some messing around but I've done it successfully before.  But only as a test.  I've never used this as a full time solution.

A while back there was a thread where someone did this and thought it was good at first, but then found that there was a variable delay between the DACs after rebooting or something.  I can't remember the details, but I think his ultimate conclusion was that it was NOT a good solution.

You could play with it, but I'm expecting you to find some problems if you go deep enough.

There are certainly DACs that have 4, 6, 8, 10, and more output channels, all in one device.  Those should work properly as they all share a clock internally, so the won't have any delay or synchronization issues.

Good luck.

Brian.

[math89]

Many thanks Brian,

Yes, I just read the same conclusions as you in some former audiophile forums

Nevertheless I made a short test by linking  two zones in JRiver.
Basically it 'makes music', but I totally agree with you that the two clocks of the DAC must be synchronized.
Jitter is already an issue, and having two DAC without clock sync would be a nonsense.

Sadly, stereo USB Audiophile DACs are not pre-designed for such issue. Specifics products exist but they cost an arm...

I opened a ticket on the web site of  AMR/iFi -the DAC manufacturer- to get their opinion about how to synchronize a multi DAC system. I will put their answer here.

Regards,
Mathieu

[blgentry]

Nevertheless I made a short test by linking  two zones in JRiver.
Basically it 'makes music', but I totally agree with you that the two clocks of the DAC must be synchronized.

Linked zones are different than I was describing.  I was describing making an aggregate audio device from Audio MIDI setup.  This has options that *supposedly* sync the clocks on the DACs.  It might be worth doing a test.

I'll be interested to hear what your DAC maker has to say.

Good luck in any case. 

Brian.

[math89]

 'was describing making an aggregate audio device from Audio MIDI setup'

What does means 'aggregate audio devise', and how can I make it .

Today I could'n link the sound volume of the two DACS, even with the option 'link zones' connected. I must setup the volume sound of each separately. Not very convenient...

Thanks,
Mathieu

[blgentry]

Open Audio MIDI setup.  This is an OS X utility located in Applications/Utilities .

From there, click the + to add a new aggregate device.  If you need more help, I'm sure you can find tutorials online to help you out.

Good luck!

Brian.

[latinim]

'was describing making an aggregate audio device from Audio MIDI setup'

What does means 'aggregate audio devise', and how can I make it .

Today I could'n link the sound volume of the two DACS, even with the option 'link zones' connected. I must setup the volume sound of each separately. Not very convenient...

Thanks,
Mathieu

Dac that allow you to manage multichannel will find many in the pro division.
Search the catalog, Apogee, Prism Sound, Rme, Motu, for example.
There are all price categories.

[mattkhan]

Linked zones are different than I was describing.  I was describing making an aggregate audio device from Audio MIDI setup.  This has options that *supposedly* sync the clocks on the DACs.  It might be worth doing a test.

I think you refer to sound drift correction aka resample?

http://apple.stackexchange.com/questions/59390/what-is-sound-drift-correction-on-os-x-and-how-should-i-use-it

[blgentry]

I think you refer to sound drift correction aka resample?

http://apple.stackexchange.com/questions/59390/what-is-sound-drift-correction-on-os-x-and-how-should-i-use-it

Yes.  It seems to be on by default when you create an aggregate device.  I used the word "supposedly" because I haven't done any real testing myself (just screwing around a bit) and I haven't researched it much.

Brian.

[math89]

Many thanks guys,

A. I could 'aggregate' the 2 iFi IDSD DAC's, connected to the Macmini through the Uptone JS2+iUSB3 supply.
    I used the JRiver Equalizer to manage the frequency cutoff between the DACS.
 As long as I only managed my Sub (47Hz cutoff frequency), I could not hear any difference from the original setting
(Original setting => active filter on the sub, and a 0.005uF capacitor at the inlet of the main speaker amps).
But when I tried to separate bass and medium sections (400Hz), the stereo became blurred and some harshness appeared in the treble.

B. Then, I contacted AMR/IFi audio to get their opinion about that. Here is their answer :
"Dear Mathieu,
Thanks for your patience, please see our Technical Department's comments:

"The clocks should be very closely synchronised, << 50ppm difference between individual DAC's, however over a long time even this difference may lead to audible issues.

There is no way to synchronise multiple DAC's that have not been explicitly equipped with an external clock sync input, these tend to be pro-audio only and in that >> 1,000 USD per 2 channels class. The upcoming iDSD Pro has clock syncronisation build in, as have comparable products from other Pro Audio manufacturers.

An alternative would be to purchase a USB multi-channel DAC, but these tend to be rare.
A multi-channel USB -> SPDIF converter (e.g. USB to 4 X SPDIF with 8 Channels) may be used with the SPDIF inputs on the iDSD micro.


Finally, a word of warning, any crossover filtering or EQ in the digital domain causes significant loss of information in the best conditions. It may be preferable (and usually with much higher fidelity) to implement a good active crossover in the analogue domain, in preference over digital/PC based solutions."


C. I'm not surprised by the first part of the answer (about synchronization of the clocks)
... But I'm indeed surprised by the second part of the answer. I thought that filtering in the digital area was 'The' solution.
We learn every day, so I must stay humble  ...

Any comment ?
Mathieu

[Arindelle]

hopefully MWilems will see this and have something to say or a link or two. I have active crossovers, but its old-school in the analogue part of my system. (the best upgrade I have ever done for what it is worth)

Their response up to the last paragraph, is exactly what I've always understood.  I mentioned multichannel dacs, which people here on this forum use to create individual cross over filters (convolution etc.) These are not USB though I believe. My understanding is these active digital crossovers can be very accurate but depend on proper 3rd party software and calibrated microphones - then these "filters" can be imported into JRiver.

here's a guide, but it really about room correction, not sure if he ever finished the guide on active crossovers or not http://yabb.jriver.com/interact/index.php?topic=87538.0 which might interest you.

Adding "straight" eq is definitely going to change the sound, but convolution and parametric eq is not the same, your just telling which frequencies to go where. So if you have three way speakers you would need a DAC that handles at least 6 using the same clock(s) (I seem to remember you need one extra for configuring, but I can't find the post right now). So not sure why they say "any" crossover filtering would cause significant loss (unless they are assuming that you want to achieve fully "active" crossovers and  have not bi-passed the passive filters in your speakers  -- you'd need to do that for fully active "biamped" playback.)

I really don't understand this MAC "aggregation" thingy so I might be behind the times, but it seems like a workaround to me and not a purist solution.

[mwillems]

The idea that digital crossovers lead to loss of information and that an analog processor would be superior is baffling and would give me pause about the bona fides of that manufacturer.  I'll be charitable and assume he was thinking specifically of DSD, which is one of the only cases where what he says is even plausibly true (and even then it's an exaggeration).  The issue there is that DSD needs to be converted to PCM in order to perform any digital manipulation at all, which will necessarily add some noise, but that's one of the challenges of the format and the amount of noise is not necessarily very significant.

Bracketing out that special case, I know of no credible authority in audio (other than Siegfried Linkwitz) who advocates for analog crossovers over digital on any basis other than lower cost in commercial systems.  When compared to high quality digital filtering (like JRiver provides) analog crossovers are inherently less capable (because of space, power, and certain inherent constraints), less accurate (because parts are never exactly on spec, and part values can vary with temperature and age), less flexible (because they can't be meaningfully altered after design), can reduce sensitivity dramatically (when passive), and can add quite significant electrical noise to the system (when active).    

High quality digital filtering allows for the creation of infinitely flexible, changeable at will, textbook filters that permit you to do all the processing in a 64-bit DSP engine while the data is still digital, which given the precision available in digital (and the unavoidable electrical noise of analog filters) will necessarily be lower noise than any analog implementation of equivalent filters (even assuming you could actually implement the filters in analog, which in some cases you could not even if you wanted to). If you have a high-quality DAC feeding an analog crossover, you can significantly reduce your overall system distortion and improve your impulse response by doing your filtering "in front" of the DAC (on the PC) using digital filters, and I've got a few binned analog signal processors to bear witness to that.  

Buy yourself a high quality multi-channel DAC, many of which are available for less than $1000, some of which are even available for around $500.  It will work far better than trying to chain two devices together, especially for a crossover where you need sub-millisecond perfect sync.  

[pschelbert]

I do active crossover digitally.

I use only one DAC on USB-port (RME Fireface UFX).
If multiple DACs work, I have no clue.

How it works.

1) design corssover digital filters. I use acourate (www.audiovero.de), whith that software you can do measurements and room-EQ as well
2) Load the filters into either JRiver or a software convolver. I use acourateconvolver (www.audiovero.de)
3) Run JRiver, play a musicfile
4) Configure JRiver as to output to "acourateasio", the ASIO driver of acourate instead to of "ASIO Fireface UFX"
5) In acourateconvolver you select output soundcard=RME Fireface UFX
6) Connect ot the Audiointerface (UFX here) the poweramps, to the poweramps each individual driver of the speaker. Cut out the internal passive crossover of the speakers. Its junk.

This works fine (I did this for Martin Logan electrostatic speakers plus added a subwoofer)

Digital filters are far better, whatever aspect you consider!

Forget that DSD, its old, from Sony in the 1990's and its not good in sound quality. Highres 96kHz/24Bit surpasses it by miles.

Linkwitz: he abandonded analog crossover now. take a look at his website:www.linkwitzlab.com

Peter